The relation between a man’s belly and his testosterone levels also applies to older men.[5] A recent study showed that men over 40 years of age with abdominal obesity have a higher incidence of testosterone deficiency, erectile dysfunction and metabolic syndrome, in proportion to belly size. The effect of waist size on testosterone levels is summarized in figure 1.

Figure 1: Effect of waist circumference on testosterone levels.[5]

As shown in the figure, a man’s belly can plummet his testosterone level by half.

Use your waist-to-height ratio as a tool to see if you may have testosterone deficiency

a study was conducted to specifically examine the utility of waist-to-height ratio for prediction of testosterone levels.

207 men aged 54–86 years were recruited on the basis of having symptoms indicative of testosterone deficiency, but who were otherwise in good health.[6] This is the first study to show that adjusting waist circumference for height (i.e. the waist-to-height ratio) improves prediction of both total and free testosterone levels, compared with either waist alone or BMI, even after adjustment for age. The correlation of the waist-to-height ratio with total testosterone levels was stronger than that of free testosterone levels (figure 2).

Figure 2: Correlation between the waist-to-height ratio and total and free testosterone levels.[6]

And indicated in figure 2, the total testosterone level for a waist-to-height ratio of 0.5, 0.6 and 0.7 is roughly 461 ng/dL (16 nmol/L), 375 ng/dL (13 nmol/L) and 288 ng/dL (10 nmol/L), respectively. Thus, the guideline “keep your waist to less than half your height” pertains to testosterone levels as well, as a waist-to-height ratio above 0.5 correlates with low testosterone levels.

If your waist-to-height ratio is over 0.5 you should check yourself for symptoms that are indicative of testosterone deficiency. You can do this with a questionnaire such as the Aging Male Symptoms (AMS) questionnaire (we give you your score for free). If both your waist-to-height ratio and AMS score is high, you definitely should get a blood test to measure your testosterone levels (ideally, both total and free testosterone).

Effect of testosterone therapy on the waist-to-height ratio

If a waist-to-height ratio above 0.5 is associated with reduced testosterone levels, and testosterone therapy reduces belly fat, then testosterone therapy should reduce the waist-to-height ratio.

A recent study investigated the effect of testosterone therapy on changes in body fat measures, including the waist-to-height ratio.[7] In an observational, prospective registry study of 656 men (mean age of 61 years) with total testosterone levels below 349 ng/dL (≤ 12.1 nmol/L) and symptoms of hypogonadism, 360 men were treated with testosterone undecanoate injections 1000 mg/12 weeks (following an initial 6-week interval) for up to 10 years. The other 296 men did not receive testosterone treatment and served as controls. Measurements were taken at least twice a year, and 8-year data were analyzed.

As shown in table 3, the baseline waist-to-height ratio was 0.6 with a corresponding testosterone level of 284 ng/dL (9.84 nmol/L).

Table 3: Baseline and changes in waist-to-height ratio and testosterone levels after 8 years of testosterone therapy with testosterone undecanoate.[7]

Waist-to-height ratio

Total testosteronelevel

Baseline (year 0)

0.6

284 ng/dL (9.84 nmol/L)

Year 8

0.55

477 ng/dL (16.53 nmol/L)

After 8 years of testosterone treatment, the waist-to-height ratio had dropped to 0.55 and the testosterone level had increased to 477 ng/dL. Figure 1 graphically illustrates the yearly changes in the waist-to-height ratio.

Summary

While relatively unknown among laypeople and most old school doctors, it is now well documented in the medical research literature that expanding bellies are associated with reduced testosterone levels in men, and that testosterone treatment reduces belly fat.

To get a more accurate indication of whether you may have a reduced testosterone level, divide your waist measure (in inches) by your height (in inches). Make it a goal to keep your waist to less than half your height.

If your waist-to-height ratio is 0.5 or above, check with the Aging Male Symptoms (AMS) questionnaire if you may have symptoms indicative of testosterone deficiency. If both your waist-to-height ratio and AMS score are high, you need to do a blood test to find out your testosterone level.

While I think every man, regarless of age, should have his testosterone levels (both total and free) checked regularly - for an explanation see "Blood Testing - why?" - the reality is that blood testing of testosterone levels is not part of routine clinical practice. Even worse, most regular doctors are reluctant to order tesosterone blood tests, especially for young men. Therefore, it is important that men are aware of conditions which indicate that they may have testosterone deficiency and warrant blood testing of testosterone levels, and point this out to their doctors. If still denied, find another doctor who is more competent.